It is known from EP 0893313 B1 to transfer varying torques to the belt reel by means of an electric motor, which can be connected via a gear to the belt reel of a seat belt retractor, depending on required safety functions and restraint functions of the seat belt.
From U.S. Pat. No. 4,655,312 it is known to measure the motor current to determine a belt webbing force exceeding a threshold value on the shoulder restraining a vehicle occupant, created by the electric motor connected to the belt reel.